A state appeals court set new guidelines for same-sex parental rights Friday, following up on last year's landmark California Supreme Court ruling, and revived an Alameda County woman's quest to become the second mother of a child she had planned to raise with her partner.

A former member of a lesbian couple can gain parental status over the objections of her ex-partner, the child's biological mother, if she meets several criteria for legal motherhood, said the Court of Appeal panel in San Francisco.

Those criteria include taking part in planning to conceive, bear and raise the child, treating the child as her own, and accepting the rights and duties of parenthood, the court said.

State law contains a preference for two parents rather than one, and both the child and the would-be co-parent have constitutional rights to a relationship with each other, Justice Linda Gemello said in the 3-0 ruling.

She also said a woman who meets the tests for co-parenthood when a child is born does not lose her parental rights, even if her partner moves away with the child immediately afterward.

"That's the main significance of this case. ... Once you have that child together and you bring that baby home, you are both parents," said Shannon Minter, legal director of the National Center for Lesbian Rights in San Francisco and a lawyer for the woman seeking parental status in the case.

"Where there is clear, documented evidence of intent that they (will) both be parents, where they in fact both act as parents, those children will be presumed to have two parents," said Deborah Wald, another lawyer for the woman.

The birth mother's attorney, Rena Lindevaldsen of Liberty Counsel, a conservative religious organization, said the mother's preference should prevail.

"Within a week of birth, she said, 'I don't want the child raised in a same-sex relationship,' " Lindevaldsen said of her client. "Who has the constitutional right to determine what happens to this child and how the child is raised? The biological mom has that right."

The state Supreme Court rejected that view in August when it ruled, in three cases, that lesbian or gay partners who plan a family and raise a child together can be considered legal co-parents after a breakup, under the same state laws that cover opposite-sex couples.

The court was the first in the nation to grant full parental rights to same-sex partners regardless of their marital status or biological connection with the children. Those rights include not only custody and visitation for the parents but also Social Security, health coverage and inheritance for the children.

Lindevaldsen said the ruling violated the constitutional rights of biological parents. She said Liberty Counsel had been unable to pursue that argument in last year's cases, but would press its position in the current case after a judge in Alameda County makes a final ruling on parental status.

The couple, identified by the court as Charisma R. and Kristina S., moved in together in August 1998 and registered as domestic partners with the state in January 2002.

Kristina gave birth to a daughter, Amalia Lynne, in April 2003 after artificial insemination. She and the child moved out of the home three months later and now live in Texas, said Wald, Charisma's lawyer. She said their home had been in southern Alameda County, but she wasn't sure of the city.

The appeals court said Kristina has allowed Charisma to see the child only twice since they left. Minter said Charisma has tried to keep in touch and sends the girl presents.

Charisma's suit for parental status, filed in 2004, was dismissed by Judge Dan Grimmer of Alameda County Superior Court before last year's state Supreme Court ruling. The appeals court reinstated the suit Friday and laid out standards for Grimmer to decide whether Charisma qualifies as a second parent -- a test that was not fully spelled out in last year's decision.

The appeals court said the judge must consider whether Charisma received the girl into her home and publicly treated her as her natural child; whether she took part in the girl's conception with the understanding that she would raise her with her partner; whether she accepted parental rights and duties after the girl was born; and whether anyone else claimed to be Amalia Lynne's second parent.

The court added, however, that those criteria were not absolute, and a judge can decide whether other circumstances justify granting or withholding co-parent status.